The present invention relates, according to an aspect thereof, to a method for controlling an automatic disk clutch, the disk clutch being arranged in a motor vehicle in order to transmit motive force from an internal combustion engine to a transmission.
The invention also relates, according to an aspect, to a computer program for carrying out said method.
Automatic or semiautomatic transmissions of the Automatic Mechanical Transmission (AMT) type have become ever more common in heavier vehicles with the increasing development of microprocessor systems, making it possible, with a control computer and a number of control devices, such as servomotors, for example, to precisely regulate the engine speed, engagement and disengagement of an automatic disk clutch between engine and gearbox, and gearbox clutch members in relation to one another, so that smooth gear changes are always achieved at the correct engine speed.
An AMT usually comprises an input shaft, an intermediate shaft, which has at least one toothed gear meshing with a toothed gear on the input shaft, and main shaft with toothed gears, which mesh with toothed gears on the intermediate shaft. The main shaft is then further connected to an output shaft coupled to the driving wheels via a prop shaft, for example. Each pair of toothed gears has a different gear ratio from another pair of gears in the gearbox. Different transmission ratios are obtained in that different pairs of gears transmit the torque from the engine to the driving wheels.
The development of computer technology has also had an impact on electronic control and feedback systems for a vehicle engine, and these systems have become more precise, faster and more adaptable to prevailing engine and environmental conditions. The entire combustion process can be precisely controlled according to any operating situation. The vehicle's throttle lever (an accelerator pedal, for example), which primarily controls the fuel supply to the engine, controls the vehicle's engine via electrical wiring and electronic signals. The throttle lever is therefore equipped with sensors for detecting the throttle lever position, that is to say what throttle opening is required.
When the driver of a vehicle with automated clutch and transmission drives down a slope without pressing the accelerator pedal and e.g. a low gear engaged (high gear ratio), the speed of the engine will end up near engine idle speed, if the engine provides a certain amount of engine braking power, enough to give at least a slight retardation of the vehicle so that eventually the engine speed will come close to the engine idle speed, which normally will initiate clutch disengagement. If the clutch in this situation is disengaged without or with only a slightly activated service brake, the vehicle will suddenly accelerate due to engine braking power drop out. In this situation, with an only slightly activated service brake, the majority of the braking power comes from the engine, which causes the sudden acceleration when the engine is disconnected from the transmission and driving wheels of the vehicle. The driver will in this situation probably feel discomfort, especially if the disengagement of the clutch is triggered by a light pressing of the brake pedal.
It is desirable to eliminate the possibility for a situation to happen where a sudden vehicle acceleration accrues due to clutch disengagement or even clutch disengagement triggered by a light pressing of the brake pedal.
The method according to an aspect of the invention is a method for controlling disengagement of an automated clutch in a vehicle, where the primary function of the clutch is to transmit motive force from an internal combustion engine arranged in the vehicle to an input shaft of a transmission arranged in the vehicle, and where engine rotational speed is controlled through a throttle control. The method is characterized in that a decrease of a first engine rotational speed limit, at which the clutch is disengaged, is initiated upon sensing that the vehicle is traveling in a down slope and zero displacement of the throttle control.
The advantage of the method according to an aspect of the invention is that the clutch will be disengaged later than normal so that an engine idle speed regulator will be activated, making the engine produce positive output torque, which decreases the effect of the engine braking torque drop out when the clutch will be disengaged. The discomfort of the driver will be decreased.
According to one embodiment of the method according to an aspect of the invention said engine idle speed regulator activation is specified. In this embodiment said first engine rotational speed limit is decreased to an engine speed which is below where an, in the vehicle arranged, engine idle speed regulator is activated and starts to inject fuel into said internal combustion engine. This decreases the uncomfortable effect of the engine braking torque drop out when the clutch is disengaged.
According to another embodiment of the method said first engine rotational speed limit is decreased to a speed where an, in the vehicle arranged, engine idle speed regulator injects an amount of fuel corresponding to a positive engine torque, which equals current retarding negative engine torque, so that total output torque from the engine is approximately zero. The vehicle accelerating effect, due to engine braking torque drop out when the clutch is disengaged, will be totally eliminated.
According to a further embodiment the method according to an aspect of the invention said decrease of a first engine rotational speed limit is initiated upon further sensing of that a service brake pedal in the vehicle is lightly pressed or not pressed at all. This will secure that the driver of the vehicle will not experience a vehicle acceleration when the brake pedal is lightly depressed. According to a further development of this embodiment, said light pressing corresponds to a displacement of up to 25% of a total possible displacement of said service brake pedal.